Credulity is the tendency to believe whatever one is told. E.g.: The lawyer then challenged the credulity of the witness. "Credulity is the mark of a feeble [weak] mind."
Gullibility is a failure of social intelligence in which a person is easily tricked or maniupulated into an ill-advised course of action. It is closely related to credulity, which is the tendency to believe unlikely propositions that are unsupported by evidence
Credibility is being worthy of belief. E.g.: “Witness credibility is measured through five categories: expertise, reliability, trustworthiness, objectivity, and dynamism. While other characteristics certainly influence perceptions of credibility, these five factors comprise the basis for believability. In order for a witness to be perceived as fully credible, all five categories must be present.”
